In general, the washing machine progresses washing, rinsing, and spinning cycles for removing dirt from laundry by using actions of detergent and water. In the washing machines, there are circulating type (pulsating type), agitating type (washing pole type), and drum type washing machines.
Each of above types of washing machines requires a motor for driving the washing machine, most of which is the BLDC motor. The BLDC motor, provided with a stator having a coil wound thereon and a rotor around the stator, for generating a rotating power when power is provided to the stator.
A related art BLDC motor will be described based on the drum type washing machine, briefly. FIG. 1 illustrates a section of a related art drum type washing machine, and FIG. 2 illustrates an enlarged view of ‘A’ part in FIG. 1.
Referring to FIGS. 1 and 2, there are a tub 3 inside of a cabinet for holding washing water, and a drum 9 inside of the tub 3 for introduction of laundry. There is a drum shaft 7 for transmission of a driving power from a BLDC motor 20 to the drum 9.
There are bearings 11 in front, and rear parts of the drum shaft 17, and a bearing housing 15 in a center part of a rear wall of the tub 3 for supporting the bearings 11. There are a supporting bracket 16 mounted on the tub 3 rear wall, and a stator 30 of the BLDC motor 20 mounted on the supporting bracket 16 with a plurality of bolts 19. There is the rotor 40 of the BLDC motor 20 mounted on a rear end part of the drum shaft 17 with a fastening bolt 18.
In the meantime, there are a door 1 in a front part of the cabinet 5, and a gasket 2 between the door 1 and the tub 3. There are hanging springs 4 between an inside of an upper part of the cabinet 5 and an upper part of an outside circumference of the tub 3, and a friction damper 10 between an inside bottom of the cabinet 5 and a lower part of the outside circumference of the tub 3, for attenuating vibration of the tub occurred during spinning.
FIG. 3 illustrates a perspective view showing the stator in FIG. 1 or 2 separately, and FIG. 4 illustrates a perspective view showing the rotor in FIG. 1 or 2, separately.
Referring to FIG. 3, the stator 30 is provided with an annular frame 31, and a plurality of core teeth 33 each extended outward from the frame 31 having a coil wound thereon.
There are fastening ribs 32 each formed as a unit with the frame 31 projected toward an inside of the frame 31 having a fastening hole 32a for mounting the stator 30 on a rear wall of the tub 3.
Referring to FIG. 4, the rotor 40 is provided with permanent magnets 41 attached to an inside, and mounted to the rear end part of the drum shaft 17 with the fastening bolt 18. According to this, the drum 9, connected to the rotor 40 directly, is rotated as the drum 9 receives the rotating power from the rotor 40 when the BLDC motor 20 is in operation.
In the drum type washing machine, the rotor 40 is rotated as a power is provided to the stator 30 to form an electric magnet which interacts with the permanent magnets 41 attached to the inside of the rotor 40, and the power transmitted to the drum shaft 17 through the rotor 40 rotates the drum 9, to carry out washing and spinning.
However, the related art drum type washing machine has a problem in that the fast alternation of polarities of the core teeth 33 in driving the BLDC motor 20 causes resonance at a certain rotation speed. Of course, the problem is occurred at other washing machines having the BLDC motor applied thereto.
FIG. 5 illustrates a graph showing a result of sound power level test (PWL test) of the related art BLDC motor for the washing machine.
That is, referring to FIG. 5, the washing machine having the related art BLDC motor 20 applied thereto shows peak noises in a range of 76 dB caused by resonance at 1360 RPM and 1550 RPM.
Moreover, the high overall noise, a mean value of the noises between the peak noises, in a range of 74 dB also drops a reliability of the product.